The present invention relates generally to interferometry and, more particularly, to the use of a source of two-frequency electromagnetic radiation and polarization responsive beam splitting and recombining materials to distinctly define the two arms of a mechanically and thermally stable interferometer. One demonstrated application is the use of the such an interferometer for thermooptic spectroscopy. This present invention is the result of a contract between the U.S. Department of Energy and the University of California (Contract No. W-7405-ENG-36).
Interferometry is utilized for a wide variety of applications. Among the most interesting are the precise measurement of birefringence and refractive index, the measurement of phase differential light scattering, the measurement of motion, the measurement of length and thickness, and spectrophotometric determinations. See, e.g., Optical Interferometry by P. Hariharan, Academic Press, New York (1985), for a general reference on interferometric techniques and their applications. In all situations, complicated apparatus is employed. A summary of spectrophotometric techniques is presented in "High-Sensitivity Spectrophotometry" by T. D. Harris, Analyt. Chem. 54, 741A (1982). A more detailed account of thermooptic spectrophotometry is given in U.S. Pat. No. 4,447,153, "Apparatus And Method For Quantitative Measurement of Small Differences In Optical Absorptivity Between Two Samples Using Differential Interferometry and The Thermooptic Effect," issued to David A. Cremers and Richard A. Keller on May 8, 1984, and in "Thermooptic-Based Differential Measurements of Weak Solute Absorptions With An Interferometer" by David A. Cremers and Richard A. Keller, Appl. Opt. 21, 1654 (1982). The apparatus described therein is very complex. Another interferometric method for measuring photothermally induced refractive index variation is described in "Photothermal Detection For Light-Scattering Material By Laser Interferometry" by L. Chen and S. Y. Zhang, Appl. Phys. Lett. 50, 1340 (1987). In "Phase Fluctuation Optical Heterodyne Spectroscopy of Gases" by Christopher C. Davis and Samuel J. Petuchowski, Appl. Opt. 20, 2539 (1981), the authors describe a complicated method for studying molecular relaxation, thermal conduction, and extremely weak absorptions in the gas phase.
Accordingly, it is an object of the present invention to provide a simple, compact, vibrationally and thermally stable interferometer.
Another object of the present invention is to provide a simple, compact, vibrationally and thermally stable apparatus for measuring differential optical absorption.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in past will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.